This proposal seeks funding for continuing studies of the structural and functional embryology of the auditory system. Embryological experiments will be conducted on the brainstem auditory pathways of the chick. They will concentrate on early embryological events involving cellular interactions that may underlie the development of topographic registry between successive regions of the auditory pathways. State-of-the-art microscopic and cell-marking methods will be used to investigate cell migration and axonal terminal field formation. Functional development will be examined in the inner ear and cochlear nucleus of gerbils. Experiments are designed to examine the development of high frequency hearing and to investigate relationships between the ontogeny of mature hearing, place- code development, and nonlinear "active" properties of the inner ear. Ontogenetic properties of otoacoustic emissions will be examined before and after elimination of the endocochlear potential in order to examine contributions of different cochlear mechanisms to the development of mature information processing by the inner ear.